Is Gravity a Force?

I better say yes or risk the wrath of standard model physicists.

According to the standard model gravity is one of the four fundamental forces – Strong, Electromagnetic, Weak, and Gravity. It’s in there with the other forces but something’s amiss.  The other forces have a particle associated with them, but gravity seems an anomaly.  It either doesn’t have a particle or we haven’t found it yet.  The strong force has its gluons, electromagnetism has photons, the weak force has W+, W, and Z0. Gravity…bupkis.  So, why is it a force?

Because it appears to affect things via, well, gravitational attraction.  Anything with mass has gravity and is attracted to anything else with mass.  When you went on a date and your hand and your date’s hand got closer and closer was it gravity? No, that’s chemistry.

Gravity was a subject of great discussion among philosophers all the way from the time of Aristotle.  Galileo Galilei recognized the relationship of distance travelled and time of a falling object.  It took the combined genius of Robert Hooke, Isaac Newton, and Edmond Halley to work out the relationship between gravity and distance.  They discovered gravity is an inverse-square force.  At twice the distance gravity is one forth as strong.  Not bad for the late 17th century.

Except for the finding that Mercury has a weird orbital discrepancy not predicted by Newton’s theory, it worked exceptionally well, and is still used for most applications today.

Then came Einstein.  He figured out Mercury’s orbital issue, a 43 arcsecond per century advance in its perihelion.

In the early 20th century Albert Einstein turned the astronomy and physics world upside down.  His general relativity theory described gravity as the phenomenon of space-time curvature around a mass.  So much for gravity as a force.  Well, that just muddied the waters for physics and astronomy, but that’s a good thing.  Competition forces the competitors to work harder, think smarter, and work on their respective theories.  OK, Newton is gone, but gravity as a force is supported by a whole slew of scientists.  Problem is, if gravity is a force, where’s its particle? And what about space-time curvature, how does mass cause space-time curvature?  Einstein called quantum entanglement “spooky action at a distance”.  I think space-time curvature is a little spooky too.

So, which is right, gravity as a force or gravity as a curvature of space-time?  The force advocates predict a particle will be found, and they call it the graviton. There is hope that upgrades to the Large Hadron Collider (LHC) will “force” that little bugger out of hiding.

Even more intriguing, a fifth force might be at play, with its own, yet to be revealed particle.  Go LHC, fun!

What’s in the Sky?

Saturn and Jupiter rise in mid-evening.  Saturn is west of Jupiter and dimmer.

Sep 16-18; 1 hour after sunset; southeast: A waxing gibbous Moon shares the sky with Saturn, then Jupiter